1. Field of the Invention
The present invention relates to a motor-driven wheel improving ride comfort of vehicles.
2. Description of the Background Art
An in-wheel motor drive unit that uses a motor as the mass of a damper and that supports the motor by a motor suspension is known (Document 1: International Patent Publication No. WO02/083446A1, Document 2: Go Nagaya et al., “Development of an In-Wheel Motor with Advanced Dynamic-Damper Mechanism (20025544)”, Proceedings of 2002 JSAE Autumn Convention, No. 83-02, The Society of Automotive Engineers of Japan, Nov. 26, 2002, pp. 9-12). The motor is coupled to a wheel of a wheel and tire unit (hereinafter referred to as wheel unit) to rotate the wheel unit. The motor suspension supports the motor to allow the motor to vibrate in the up-and-down direction of the vehicle's body and separates the motor from unsprung weights. The wheel is supported on the vehicle's body by a suspension arm. Regarding this in-wheel motor drive system, as the wheel unit vibrates, the vibrations are transmitted through the wheel to the motor to cause the motor to vibrate in the up-and-down direction of the vehicle's body. The vibrations of the motor cancel vibrations of unsprung components. Here, a flexible coupling is used for smoothly transmitting power generated by the motor to the wheel unit even if respective rotational axes of the motor and the wheel unit become eccentric from each other.
In the case where the motor is mounted to serve as the dynamic damper as mentioned above, the motor swings and moreover an axial force is exerted on the motor when the vehicle corners. Then, such an axial force has to be supported.
For supporting the motor in the axial direction, an outer race of a constant-velocity joint and a wheel hub may be integrated into a single part. In this case, however, it is necessary to avoid an increase in diameter of a hub bearing as well as deterioration in ease of installation of a snap ring serving to axially restrict an output shaft transmitting motor torque and an inner race of the constant-velocity joint. Accordingly, some considerations have to be taken regarding the axial support of the motor.